This invention relates to variable capacity vane compressors which are adapted for use as refrigerant compressors of air conditioners for automotive vehicles.
A variable capacity vane compressor is known e.g. by Japanese Provisional Utility Model Publication (Kokai) No. 55-2000 filed by the same assignee of the present application, which is capable of controlling the capacity of the compressor by varying the suction quantity of a gas to be compressed. According to this known vane compressor, arcuate slots are formed in a peripheral wall of the cylinder and each extend from a lateral side of a refrigerant inlet port formed through the same peripheral wall of the cylinder and also through an end plate of the cylinder, and in which is slidably fitted a throttle plate, wherein the effective circumferential length of the opening of the refrigerant inlet port is varied by displacing the throttle plate relative to the slot so that the compression commencing position in a compression chamber defined in the cylinder and accordingly the compression stroke period varies to thereby vary the capacity or delivery quantity of the compressor. A link member is coupled at one end to the throttle plate via a support shaft secured to the end plate,and at the other end to an actuator so that the link member is pivotally displaced by the actuator to displace the throttle plate.
However, according to the conventional vane compressor, because of the intervention of the link member between driving means or the actuator and a control element or the throttle plate for causing displacement of the trottle plate, the thorttle plate undergoes a large hysteresis, leading to low reliability in controlling the compressor capacity, and also the capacity control mechanism using the link member, etc. requires complicated machining and assemblage.
To solve the above problem, a variable capacity vane compressor has been proposed e.g. by Japanese Patent Application No. 60-160760, which comprises a front side block which has an end face facing the rotor and formed with an annular recess and additional refrigerant inlet ports continuous with the annular recess and communicating respective compression chambers within the cylinder with the suction chamber, an annular control element rotatably received within the annular recess, and means responsive to a differential pressure between a high pressure such as discharge refrigerant pressure and a low pressure such as suction refrigerant pressure for causing rotation of the annular control element, wherein the rotation of the control element causes the openings of the additional inlet ports and accordingly the compression stroke period to vary to thereby vary the capacity of the compressor.
However, according to this proposed variable capacity compressor, there is provided a considerable clearance between the rotor and the control element which amounts to the sum of a first clearance for allowing smooth rotation of the rotor and a second clearance for allowing smooth rotation of the control element. The presence of such large clearance causes an apreciable amount of refrigerant to leak from the compression chambers into the suction chamber through the clearance an the additional refrigerant inlet ports, which necessitates a great driving force for rotating the rotor, resulting undesirable heat generation in sliding parts of the compressor and increased temperature of the discharged refrigerant.
Furthermore, in vane compressors in general pressure within a high pressure chamber is supplied to radially inner end faces of the vanes as back pressure to maintain steady contact of tips of the vanes with the inner peripheral or camming surface of the cam ring. However, according to the aforesaid conventional vane compressors adapted to vary the compression commencing position, when the compression stroke period is reduced to decrease the capacity, the back pressure applied to the vanes correspondingly decreases, causing chattering of the vanes, i.e. alternate jumping and hitting of the vanes off and against the camming inner peripheral surface of the cam ring, resulting in degraded compression efficiency. If the supply amount of pressure from the high pressure chamber to the vanes is set at a larger value so as to obtain sufficient back pressure to be applied to the vanes when the compression stroke period is reduced to decrease the capacity, excessive back pressure is applied to the vanes when the compression stroke period is increased to increase the capacity, resulting in increased sliding friction and hence increased loss of power.
Moreover, to enhance the reliability of control of the capacity of variable capacity vane compressors of the aforesaid type it is desirable that sliding displacement of the control element or throttle plate in the slot should take place smoothly and promptly or with high responsiveness to operating conditions of the compressor.